Method and system for forming an air gap structure

ABSTRACT

A method for forming an air gap structure on a substrate is described. The method comprises forming a sacrificial layer on a substrate, wherein the sacrificial layer comprises a decomposable material that thermally decomposes at a thermal decomposition temperature above approximately 350 degrees C. Thereafter, a cap layer is formed on the sacrificial layer at a substrate temperature less than the thermal decomposition temperature of the sacrificial layer. The sacrificial layer is decomposed by performing a first exposure of the substrate to ultraviolet (UV) radiation and heating the substrate to a first temperature less than the thermal decomposition temperature of the sacrificial layer, and the decomposed sacrificial layer is removed through the cap layer. The cap layer is cured to cross-link the cap layer by performing a second exposure of the substrate to UV radiation and heating the substrate to a second temperature greater than the first temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to pending U.S. patent application Ser. No.11/269,581, entitled “MULTI-STEP SYSTEM AND METHOD FOR CURING ADIELECTRIC FILM”, filed on Nov. 9, 2005; pending U.S. patent applicationSer. No. 11/517,358, entitled “THERMAL PROCESSING SYSTEM FOR CURINGDIELECTRIC FILMS”, filed on Sep. 8, 2006; and co-pending U.S. patentapplication Ser. No. 11/873,977, entitled “METHOD FOR AIR GAP FORMATIONUSING UV-DECOMPOSABLE MATERIALS” (Docket No. TDC-001) filed on Oct. 17,2007. The entire contents of these applications are herein incorporatedby reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and system for forming an air gapstructure on a substrate and, more particularly, to a method and systemfor decomposing and removing a sacrificial layer through a cap layerusing a first ultraviolet (UV) radiation process, and curing the caplayer using a second UV radiation process.

2. Description of Related Art

As is known to those in the semiconductor art, interconnect delay is amajor limiting factor in the drive to improve the speed and performanceof integrated circuits (IC). One way to minimize interconnect delay isto reduce inter-connect capacitance by using low dielectric constant(low-k) materials as the insulating dielectric for metal wires in the ICdevices. Thus, in recent years, low-k materials have been developed toreplace relatively high dielectric constant insulating materials, suchas silicon dioxide. In particular, low-k films are being utilized forinter-level and intra-level dielectric layers between metal wires insemiconductor devices.

Additionally, in order to further reduce the dielectric constant ofinsulating materials, material films are formed with pores, i.e., porouslow-k dielectric films. Such low-k films can be deposited by a spin-ondielectric (SOD) method similar to the application of photo-resist, orby chemical vapor deposition (CVD). Thus, the use of low-k materials isreadily adaptable to existing semiconductor manufacturing processes.

Furthermore, in yet another attempt to reduce the dielectric constant ofinsulating materials, air gap structures are contemplated. Air gapstructures are formed by depositing a sacrificial material on asubstrate and then depositing a bridging material over the sacrificialmaterial. Thereafter, at a later point in the device manufacturingprocess, the sacrificial material is decomposed and removed in order toleave a gap or void in its absence. Conventionally, the sacrificialmaterial is removed using a chemical or thermal process.

However, despite the promise of superior electrical performance by thisapproach, the mechanical stability is a primary concern. In particular,when the bridging materials, which may include porous low-k materials,are formed, these materials have been observed to collapse duringdecomposition and subsequent process steps. Furthermore, the selectionof a sacrificial material, the selection of a bridging material, and theprocesses for preparing, forming and integrating these materials posenumerous challenges for the successful implementation of an air gapstructure in an IC device.

SUMMARY OF THE INVENTION

The invention relates to a method and system for forming an air gapstructure on a substrate. More particularly, the invention relates to amethod and system for decomposing and removing a sacrificial layerthrough a cap layer using a first ultraviolet (UV) radiation process,and curing the cap layer using a second UV radiation process.

According to an embodiment, a method for forming an air gap structure ona substrate is described. The method comprises forming a sacrificiallayer on a substrate, wherein the sacrificial layer comprises adecomposable material that thermally decomposes at a thermaldecomposition temperature above approximately 350 degrees C. Thereafter,a cap layer is formed on the sacrificial layer at a substratetemperature less than the thermal decomposition temperature of thesacrificial layer. The sacrificial layer is decomposed by performing afirst exposure of the substrate to ultraviolet (UV) radiation andheating the substrate to a first temperature less than the thermaldecomposition temperature of the sacrificial layer, and the decomposedsacrificial layer is removed through the cap layer. The cap layer iscured to cross-link the cap layer by performing a second exposure of thesubstrate to UV radiation and heating the substrate to a secondtemperature greater than the first temperature.

According to another embodiment, a processing system for preparing anair gap structure on a substrate is described, comprising: a processingchamber configured to provide a vacuum environment for a substrate; asubstrate holder coupled to the processing chamber, and configured tosupport the substrate; a first ultraviolet (UV) radiation sourceconfigured to expose the substrate to a first spectrum of UV radiation;a second ultraviolet (UV) radiation source configured to expose thesubstrate to a second spectrum of UV radiation; and a heating deviceconfigured to elevate the temperature of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a flow chart of a method of removing a sacrificial material ona substrate;

FIG. 2 is a flow chart of a method of removing a sacrificial material ona substrate;

FIG. 3 is a flow chart of a method of forming an air gap structure on asubstrate according to an embodiment;

FIGS. 4A through 4E illustrate a method of forming an air gap structureon a substrate according to an embodiment;

FIG. 5 is a schematic cross-sectional view of a processing systemaccording to an embodiment; and

FIG. 6 presents exemplary data for decomposing a sacrificial material.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following description, in order to facilitate a thoroughunderstanding of the invention and for purposes of explanation and notlimitation, specific details are set forth, such as a particular processand descriptions of various systems and components within which such aprocess may be performed. However, it should be understood that theinvention may be practiced in other embodiments that depart from thesespecific details.

As described above, air gap structures are contemplated for furtherreducing interconnect capacitance and, in turn, reducing interconnectdelay and improving the speed and performance of integrated circuits(IC). Therein, bridging material is formed over sacrificial material,and the sacrificial material is decomposed and removed in order to leavea gap or void in its absence. Also, as described above, when thebridging materials, which overlie the sacrificial material, are formed,these materials have been observed to collapse during decomposition ofthe sacrificial material and subsequent process steps. Therefore, amethod and system is described for forming an air gap structure on asubstrate that has greater mechanical strength.

Referring to FIG. 1, a method of selectively removing a sacrificialmaterial on a substrate is described. The method comprises a flow chart100 beginning in 110 with forming a sacrificial layer on a substrate.The sacrificial layer may be formed using a vapor deposition process,such as an initiated chemical vapor deposition (iCVD) process asdescribed in greater detail below. Thereafter, in 120, the sacrificiallayer is selectively decomposed at a temperature less than thetemperature required to thermally decompose the sacrificial layer,wherein the selective decomposition is performed by selectively exposingthe sacrificial layer to UV radiation. The temperature required tothermally decompose the sacrificial layer can vary depending upon thechemical composition of the sacrificial layer, and the dimensions of thesacrificial layer. For example, the temperature required to thermallydecompose the sacrificial layer can be different for a patterned filmversus a blanket film.

By selectively decomposing the sacrificial material, the sacrificialmaterial may be retained in regions on the substrate where greatermechanical strength is desired (e.g., wide spacing of metal lines in ICdevices), and the sacrificial material may be removed in regions on thesubstrate where less mechanical strength is desired (e.g., close spacingof metal lines in IC devices). In regions on the substrate where greatermechanical strength is desired (e.g., wide spacing of metal lines in ICdevices), the demand for lower dielectric constant (to lower the linecapacitance) is less (due to, for example, the wider spacing), whereasin regions on the substrate where less mechanical strength is desired(e.g., close spacing of metal lines in IC devices), the demand for lowerdielectric constant (to lower the interconnect line capacitance) isgreater (due to, for example, the closer spacing). Alternatively, thesacrificial layer may not be selectively decomposed, and rather thesacrificial layer may be non-selectively decomposed, i.e., substantiallythe entire sacrificial layer is subjected to a decomposition process byexposing the sacrificial layer to UV radiation at a temperature lessthan the temperature required to thermally decompose the sacrificiallayer.

For example, the method may comprise forming the sacrificial layer onthe substrate, wherein the sacrificial layer comprises a decomposablematerial that thermally decomposes at a thermal decompositiontemperature above approximately 325 degrees C. Once the sacrificialmaterial is formed, a cap layer is formed over the sacrificial materialto serve as the bridging material. Thereafter, the sacrificial materialis selectively decomposed at specific regions on the substrate ornon-selectively decomposed by selectively or non-selectively exposingthe sacrificial layer to ultraviolet (UV) radiation and heating thesubstrate to a UV-assisted decomposition temperature less than thethermal decomposition temperature of the sacrificial layer. The methodmay further comprise selectively exposing the sacrificial layer at thespecific regions on the substrate to infrared (IR) radiation, ornon-selectively exposing the sacrificial layer to infrared (IR)radiation.

The inventors have recognized that a UV-assisted decomposition processis more efficient in energy transfer, as compared to purely thermaldecomposition processes, and the higher energy levels found in the formof energetic photons can facilitate the decomposition of a sacrificialmaterial at a temperature less than its thermal decompositiontemperature. Since the temperature of the sacrificial layer does notexceed its thermal decomposition temperature, the sacrificial layer maybe selectively decomposed by selectively assisting the decompositionprocess at specific regions through selective exposure to UV radiationor non-selectively decomposed by non-selectively assisting thedecomposition process through non-selective exposure to UV radiation.

Referring now to FIG. 2, a method of selectively removing a sacrificialmaterial on a substrate is described. Although the method is describedfor selectively removing a sacrificial material on a substrate, themethod may be utilized for non-selectively removing a sacrificial layeron a substrate. The method comprises a flow chart 200 beginning in 210with depositing a sacrificial layer on a substrate. The sacrificiallayer may be formed using a vapor deposition process, such as aninitiated chemical vapor deposition (iCVD) process as described ingreater detail below.

In 220, a cap layer is deposited on the sacrificial layer, wherein thecap layer comprises a porous material. The cap layer may be formed usinga vapor deposition process, such as a chemical vapor deposition (CVD)process as described in greater detail below.

Thereafter, in 230, the cap layer and the sacrificial layer arepatterned with a structure comprising a via structure, a trenchstructure, or a trench-via structure, or a combination thereof. Thepatterning process may include a wet developing process, a drydeveloping process, a wet etch process, or a dry etch process, or anycombination of two or more thereof. For example, such processes would beunderstood by one skilled in the art of preparing and using alithographic mask, with or without one or more soft mask layers or hardmask layers, to etch a pattern into one or more dielectric layers toform the structure.

In 240, the structure is metallized, wherein at least a portion of thecap layer is exposed. The metallization process may include conformallydepositing a barrier layer on the substrate, filling the structure withmetal, performing a pre-planarization anneal process, and planarizingthe metallized structure to the cap layer in order to expose the caplayer. For example, the metallization process may include a damasceneprocess, or a dual damascene process.

In 250, once the metallized structure is formed, a UV exposure masklayer is formed on the cap layer, wherein the UV exposure mask layercomprises an exposure pattern for decomposing the sacrificial layer. Forexample, the UV exposure mask layer may comprise a non-criticallithographic mask prepared using conventional lithographic procedures.If non-selective removal of the sacrificial layer is desired, then theUV exposure mask may not be necessary.

In 260, the sacrificial layer and the cap layer are exposed to UVradiation in order to selectively decompose the sacrificial layeraccording to the exposure pattern at a temperature less than thetemperature required to thermally decompose the sacrificial layer.

Referring now to FIG. 3, a method for forming an air gap structure on asubstrate is described according to another embodiment. The methodcomprises a flow chart 300 beginning in 310 with preparing a substratecomprising a sacrificial layer and a cap layer formed on the sacrificiallayer.

Thereafter, in 320, the substrate is disposed in a processing system.The processing system may be configured to support the substrate whileproviding a contaminant-free, low pressure (e.g., sub-atmospheric)environment. Furthermore, the processing system may be configured toirradiate the substrate with ultraviolet radiation and optionallyinfrared (IR) radiation. Moreover, the processing system may beconfigured to heat the substrate and control the temperature of thesubstrate.

In 330, the sacrificial material is exposed to a first UV radiationprocess in order to decompose the sacrificial material and cause theremoval of the sacrificial material through the cap layer. The UVradiation for the first exposure process is selected in order todecompose the sacrificial material and partially cure the cap layer. Theinventors have observed that partial curing of the cap layer during thefirst UV radiation exposure is acceptable, as long as that cross-linkingin the sacrificial material is reduced or minimized. Excessivecross-linking of the cap layer during the first UV exposure can causedifficulty in removing the decomposed sacrificial material through thecap layer.

In 340, the cap layer is exposed to a second UV radiation process inorder to substantially remove decomposed sacrificial material trapped inthe cap layer and substantially complete the curing of the cap layer.The curing of the cap layer during the second UV exposure process mayserve to mechanically strengthen the cap layer.

When preparing an air gap structure, the cap layer, which bridges theair gap or void, may comprise a low-k dielectric material or anultra-low-k (ULK) dielectric material. Furthermore, the cap layer maycomprise a porous ULK dielectric material.

The cap layer may have a dielectric constant value (before drying and/orcuring, or after drying and/or curing, or both) equal to or less thanthe dielectric constant of SiO₂, which is approximately 4 (e.g., thedielectric constant for thermal silicon dioxide can range from 3.8 to3.9). In various embodiments of the invention, the cap layer may have adielectric constant (before drying and/or curing, or after drying and/orcuring, or both) of less than 3.0, a dielectric constant of less than2.5, or a dielectric constant ranging from 1.6 to 2.7.

Low-k materials are less robust than more traditional silicon dioxide,and the mechanical strength deteriorates further with the introductionof porosity. The porous low-k films can easily be damaged during plasmaprocessing, thereby making desirable a mechanical strengthening process(or curing process). It has been understood that enhancement of thematerial strength of porous low-k dielectrics is essential for theirsuccessful integration. Aimed at mechanical strengthening, curingtechniques are being explored to make porous low-k films more robust andsuitable for integration.

The curing of a low-k film includes a process whereby a thin filmdeposited for example using spin-on or vapor deposition (such aschemical vapor deposition CVD) techniques, is treated in order to causecross-linking within the film. During the curing process, free radicalpolymerization is understood to be the primary route for cross-linking.As polymer chains cross-link, mechanical properties, such as the Young'smodulus, the film hardness, the fracture toughness and the interfacialadhesion, are improved, thereby improving the fabrication robustness ofthe low-k film (i.e., the cap layer).

Referring now to FIGS. 4A through 4E, a method of removing a sacrificialmaterial and a method of forming an air gap structure are illustrated.In FIG. 4A, an exploded view of a circuit level on a portion of asubstrate is depicted. The substrate comprises metal interconnects 10having a metal line 12 and a metal via 14 that connects metal line 12with electrical circuitry underlying the depicted circuit level. Eachmetal via 14 is electrically insulated from the next metal via 14 by vialevel dielectric layer 20, and each metal line 12 is electricallyinsulated from the next metal line 12 by line level dielectriccomprising a sacrificial layer 30 and a cap layer 40. Once thesacrificial layer 30 is removed, an air gap structure having the caplayer 40 as the bridging material remains as the line level dielectricfor portions of the substrate. Further, a liner 16 comprising a barriermaterial may be deposited between the insulating dielectrics and themetal lines 12 and metal vias 14.

Additionally, as shown in FIG. 4A, the spacing between metal lines 12may vary across the substrate. For example, the spacing between metallines 12 can be (relatively) narrow in a first region 50, while thespacing can be (relatively) wide in a second region 55. In regions wherethe spacing is relatively narrow, the necessity for a lower dielectricconstant of the insulating material may be greater in order tocompensate for the closer spacing and, therefore, an air gap structuremay be formed. In regions where the spacing is relatively wide, thenecessity for a lower dielectric constant may be less and, hence, thesacrificial material may be retained in the structure in order topreserve mechanical strength. Alternatively, the spacing between metallines 12 may not vary across the substrate.

The substrate, to be treated, may be a semiconductor, a metallicconductor, or any other substrate to which the air gap structure is tobe formed upon. The cap layer 40 comprises a dielectric material thatmay have a dielectric constant value equal to or less than thedielectric constant of SiO₂, which is approximately 4 (e.g., thedielectric constant for thermal silicon dioxide can range from 3.8 to3.9). In various embodiments of the invention, the cap layer 40 may havea dielectric constant of less than 3.0, a dielectric constant of lessthan 2.5, or a dielectric constant ranging from 1.6 to 2.7.

The cap layer 40 may be described as a low dielectric constant (low-k)film or an ultra low-k film. The cap layer 40 may include a porousdielectric film, or it may include a non-porous dielectric film.However, in the latter, the cap layer 40 should allow the removal of thesacrificial layer 30 during it's decomposition. For instance, if the caplayer 40 includes a non-porous material, then one or more openings maybe formed to permit the passage of the decomposed sacrificial material.As an example, the cap layer 40 may include a dual phase porous low-kfilm. The dielectric constant of the cap layer 40 may have a higherdielectric constant prior to porogen burn-out than following porogenburn-out.

The cap layer 40 can be formed using chemical vapor deposition (CVD)techniques, or spin-on dielectric (SOD) techniques such as those offeredin the Clean Track ACT 8 SOD and ACT 12 SOD coating systems commerciallyavailable from Tokyo Electron Limited (TEL). The Clean Track ACT 8 (200mm) and ACT 12 (300 mm) coating systems provide coat, bake, and curetools for SOD materials. The track system can be configured forprocessing substrate sizes of 100 mm, 200 mm, 300 mm, and greater. Othersystems and methods for forming a dielectric film on a substrate asknown to those skilled in the art of both spin-on dielectric technologyand CVD dielectric technology are suitable for the invention.

As described above, the cap layer 40 may be characterized as a lowdielectric constant (or low-k) dielectric film. The cap layer 40 mayinclude at least one of an organic, inorganic, and inorganic-organichybrid material. Additionally, the cap layer 40 may be porous ornon-porous. For example, the cap layer 40 may include an inorganic,silicate-based material, such as oxidized organosilane (or organosiloxane), deposited using CVD techniques. Examples of such filmsinclude Black Diamond™ CVD organosilicate glass (OSG) films commerciallyavailable from Applied Materials, Inc., or Coral™ CVD films commerciallyavailable from Novellus Systems. Additionally, for example, the caplayer 40 can include single-phase materials, such as a siliconoxide-based matrix having terminal organic side groups that inhibitcross-linking during a curing process to create small voids (or pores).Additionally, for example, the cap layer 40 can include dual-phasematerials, such as a silicon oxide-based matrix having inclusions oforganic material (e.g., a porogen) that is decomposed and evaporatedduring a curing process. Alternatively, the cap layer 40 may include aninorganic, silicate-based material, such as hydrogen silsesquioxane(HSQ) or methyl silsesquioxane (MSQ), deposited using SOD techniques.Examples of such films include FOx HSQ commercially available from DowCorning, XLK porous HSQ commercially available from Dow Corning, and JSRLKD-5109 commercially available from JSR Microelectronics. Stillalternatively, the cap layer 40 can include an organic materialdeposited using SOD techniques. Examples of such films include SiLK-I,SiLK-J, SiLK-H, SiLK-D, porous SiLK-T, porous SiLK-Y, and porous SiLK-Zsemiconductor dielectric resins commercially available from DowChemical, and FLARE™, and Nano-glass commercially available fromHoneywell.

The sacrificial layer 30 comprises a decomposable polymer. The polymermay comprise cross-linked polymers. Additionally, the sacrificial layer30 may comprise a thermally degradable polymer having thermal propertiesthat may be tunable based upon selection of it's chemical structure.

The decomposable polymer can be formed using a polymerization processthat utilizes one or more monomers and optionally one or moreinitiators, wherein the one or more initiators may cause thedissociation or fragmentation of the one or more monomers, thus formingreactive monomers. Additionally, one or more cross-linking agents may beutilized to facilitate or assist the polymerization process on thesubstrate. For example, the polymerization process may include initiatedchemical vapor deposition (iCVD). Additional details on an iCVD processare described in pending U.S. Patent Application Publication No. US2007/0032620 A1, entitled “Chemical Vapor Deposition of Hydrogel Films”.Further details on iCVD hardware are described in pending U.S. patentapplication Ser. No. 11/693,067, entitled “Vapor Deposition System andMethod of Operating”.

The one or more monomers may comprise a methacrylate monomer. A monomercan have various side groups, including phenyls, ethers, silyl/siloxylgroups, amides, and unsaturated and saturated hydrocarbon groups.

The one or more cross-linking agents may comprise difunctional acrylatecross-linkers or methacrylate cross-linkers.

According to one example, the sacrificial layer 30 may compriseP(npMA-co-EGDA), wherein P(npMA) (poly (neopentyl methacrylate))represents the monomer and EGDA (ethylene glycol diacrylate) representsthe cross-linking agent. Referring to FIG. 6, exemplary data is providedfor a sacrificial layer comprising P(npMA-co-EGDA). The removalpercentage (%) of the sacrificial layer is illustrated as a function ofthe temperature (degrees C.) of the substrate holder upon which thesubstrate having the sacrificial layer rests, wherein no UV radiation isutilized to assist the decomposition process. From inspection of FIG. 6,decomposition of the sacrificial layer initiates at approximately 300degrees C., and only a marginal amount of the sacrificial layer (about16%) is removed at 375 degrees C.

Now referring to Table 1, additional exemplary data is provided forP(npMA-co-EGDA), wherein UV radiation is utilized to assist thedecomposition process. As shown in Table 1, the thickness change of asacrificial layer (%) is provided as a function of the wavelength of UVradiation in nanometers (nm) and the substrate holder temperature(degrees C.). From inspection of the data, the absence of UV radiationat a substrate holder temperature of 300 degrees C. produces anegligible change in thickness of the sacrificial layer (i.e.,negligible decomposition). However, the irradiation of the sacrificiallayer with UV radiation, coupled with elevation of the substrate holdertemperature to 300° C., causes a substantial increase in the thicknesschange of the sacrificial layer. In particular, at shorter UVwavelengths (i.e., more energetic photons), the decomposition process ismore effective at the (relatively) lower temperature (that is less thanthe temperature where thermal decomposition readily occurs), and anappreciable change in the thickness of the sacrificial layer is achieved(i.e., −72% at 172 nm).

TABLE 1 Substrate holder UV Radiation temperature Thickness changeWavelength (nm) (degrees C.) after 15 minutes (%) None 300 −2 172 300−72 222 300 −66 308 300 −16 308 280 −13

The via level dielectric layer 20 comprises a dielectric material thatmay have a dielectric constant value equal to or less than thedielectric constant of SiO₂, which is approximately 4 (e.g., thedielectric constant for thermal silicon dioxide can range from 3.8 to3.9). In various embodiments of the invention, the via level dielectriclayer 20 may have a dielectric constant of less than 3.0, a dielectricconstant of less than 2.5, or a dielectric constant ranging from 1.6 to2.7. The via level dielectric layer 20 may be described as a lowdielectric constant (low-k) film or an ultra low-k film. The via leveldielectric layer 20 may include a porous dielectric film, or it mayinclude a non-porous dielectric film. For example, the via leveldielectric layer 20 may include any one of the dielectric materialsdescribed above.

The metal lines 12 may comprise copper (Cu) or aluminum (Al) oraluminum-copper alloy, for example. Similarly, the metal vias 14 maycomprise Cu or Al or aluminum-copper alloy, for example. The liner 16may comprise tantalum (Ta), tantalum nitride (TaN_(x)), tantalumcarbonitride (TaC_(x)N_(y)), Cu, ruthenium (Ru), or any material knownto be used as a barrier layer or seed layer.

Optionally, following the formation of the cap layer 40, the cap layer40 may be treated by a drying process in order to remove, or reduce tosufficient levels, one or more contaminants in the dielectric film,including, for example, moisture, solvent, porogen, or any othercontaminant that may interfere with a curing process.

For example, a sufficient reduction of a specific contaminant presentwithin the dielectric film, from prior to the drying process tofollowing the drying process, can include a reduction of approximately10% to approximately 100% of the specific contaminant. The level ofcontaminant reduction may be measured using Fourier transform infrared(FTIR) spectroscopy, or mass spectroscopy. Alternatively, for example, asufficient reduction of a specific contaminant present within thedielectric film can range from approximately 50% to approximately 100%.Alternatively, for example, a sufficient reduction of a specificcontaminant present within the dielectric film can range fromapproximately 80% to approximately 100%.

Referring now to FIG. 4B, the sacrificial layer 30 and the cap layer 40are exposed to a first UV radiation process 32 in order to decompose thesacrificial layer 30 and cause the removal of the sacrificial layer 30through the cap layer 40. The first UV radiation process 32 is selectedin order to decompose the sacrificial layer 30 and partially cure thecap layer 40. However, substantially no curing to minimal curing of thecap layer 40 is also acceptable. The inventors have observed thatpartial curing of the cap layer 40 during the first UV radiationexposure is acceptable, permitted that cross-linking in the sacrificialmaterial is reduced or minimized. Excessive cross-linking of the caplayer during the first UV exposure can cause difficulty in removing thedecomposed sacrificial material through the cap layer 40.

The inventors have recognized that the energy level (hν) and the ratethat energy is delivered (q′) to the cap layer 40 during decompositionof the sacrificial layer 30 varies at different stages of the curingprocess. The curing process can include mechanisms for generation ofcross-link initiators, burn-out of porogens, decomposition of porogens,film cross-linking, and optionally cross-link initiator diffusion. Eachmechanism may require a different energy level and rate at which energyis delivered to the dielectric film. For instance, during the curing ofthe matrix material, cross-link initiators may be generated using photonand phonon induced bond dissociation within the matrix material. Bonddissociation can require energy levels having a wavelength less than orequal to approximately 300 to 400 nm. Additionally, for instance,porogen burn-out may be facilitated with photon absorption by thephotosensitizer. Porogen burn-out may require UV wavelengths, such aswavelengths less than or equal to approximately 300 to 400 nm. Furtheryet, for instance, cross-linking can be facilitated by thermal energysufficient for bond formation and reorganization. Bond formation andreorganization may require energy levels having a wavelength ofapproximately 9 microns which, for example, corresponds to the mainabsorbance peak in siloxane-based organosilicate low-k materials.

The first exposure of the sacrificial layer 30 and the cap layer 40 toUV radiation may include exposing these layers to UV radiation from oneor more UV lamps, one or more UV LEDs (light emitting diodes), or one ormore UV lasers, or a combination of two or more thereof. The wavelengthof the UV radiation may be less than or equal to approximately 350 nm.Desirably, the UV radiation may range in wavelength from approximately150 nm to approximately 350 nm and, more desirably, the UV radiation mayrange in wavelength from approximately 170 nm to approximately 320 nm orfrom approximately 170 nm to approximately 240 nm).

During the first exposure of the sacrificial layer 30 and the cap layer40 to UV radiation, these layers may be thermally treated by elevatingthe temperature of the substrate to a UV-assisted decompositiontemperature less than the temperature required to thermally decomposethe sacrificial layer 30 in the absence of UV radiation. The thermaldecomposition temperature may be greater than or equal to 350 degreesC., or it may be greater than approximately 375 degrees C.Alternatively, the thermal decomposition temperature may be greater thanor equal to approximately 400 degrees C., or it may be greater thanapproximately 425 degrees C. The UV-assisted decomposition temperatureis selected to be less than the thermal decomposition temperature. Forexample, the UV-assisted decomposition temperature may be less than orequal to approximately 375 degrees C., or it may be less than or equalto approximately 350 degrees C. Alternatively, for example, theUV-assisted decomposition temperature may be less than or equal toapproximately 325 degrees C., or it may be less than or equal toapproximately 300 degrees C.

Optionally, during the first exposure of the sacrificial layer 30 to UVradiation, the sacrificial layer 30 and the cap layer 40 may be exposedto infrared (IR) radiation. The exposure of the sacrificial layer 30 andthe cap layer 40 to IR radiation may include exposing these layers to IRradiation from one or more IR lamps, one or more IR LEDs, or one or moreIR lasers, or a combination of two or more thereof. The IR radiation mayrange in wavelength from approximately 1 micron to approximately 25microns. Desirably, the IR radiation may range in wavelength fromapproximately 8 microns to approximately 14 microns.

As illustrated in FIG. 4B, the sacrificial layer 30 may be selectivelydecomposed at specific regions on the substrate by selectively exposingthe sacrificial layer at the specific regions on the substrate to UVradiation and heating the substrate to a UV-assisted decompositiontemperature less than the thermal decomposition temperature of thesacrificial layer 30. For instance, in FIG. 4B, the sacrificial layer 30is exposed to UV radiation and decomposed in the first region 50, whileit is not exposed to UV radiation and decomposed in the second region55. The method may further comprise selectively exposing the sacrificiallayer 30 at the specific regions on the substrate to infrared (IR)radiation. Alternatively, the sacrificial layer 30 may benon-selectively decomposed on the substrate by non-selectively exposingthe sacrificial layer on the substrate to UV radiation and heating thesubstrate to a UV-assisted decomposition temperature less than thethermal decomposition temperature of the sacrificial layer 30.Furthermore, the method may further comprise non-selectively exposingthe sacrificial layer 30 on the substrate to infrared (IR) radiation.

When selectively exposing the sacrificial layer 30 to UV radiation, a UVexposure mask layer may be formed on the cap layer 40, wherein the UVexposure mask layer comprises an exposure pattern for decomposing thesacrificial layer 30. For example, the UV exposure mask layer maycomprise a non-critical lithographic mask prepared using conventionallithographic procedures.

Referring now to FIG. 4C, the first UV radiation process facilitates thedecomposition of the sacrificial layer 30. As the sacrificial layer 30decomposes, the sacrificial layer 30 is removed through the cap layer40, thus, leaving air gap 34.

Referring now to FIG. 4D, the cap layer 40 is exposed to a second UVradiation process 42 in order to substantially remove decomposedsacrificial material trapped in the cap layer 40 and substantiallycomplete the curing of the cap layer 40 to produce cured cap layer 44(as shown in FIG. 4E). The curing of the cap layer 40 during the secondUV radiation process may serve to mechanically strengthen the cap layer40.

The second exposure of the cap layer 40 to UV radiation may includeexposing the cap layer 40 to UV radiation from one or more UV lamps, oneo more UV LEDs, or one or more UV lasers, or a combination of two ormore thereof. The wavelength of the UV radiation may be less than orequal to approximately 350 nm. Desirably, the UV radiation may range inwavelength from approximately 100 nm to approximately 300 nm and, moredesirably, the UV radiation may range in wavelength from approximately150 nm to approximately 240 nm. According to one embodiment, the UVradiation for the second UV radiation process comprises wavelengthsshorter than those during the first UV radiation process (e.g., higherenergy to promote cross-linking of the cap layer 40).

During the second exposure of the cap layer 40 to UV radiation, the caplayer 40 may be thermally treated by elevating the temperature of thesubstrate to a UV-assisted cure temperature less than the temperaturerequired to thermally decompose the sacrificial layer 30.

During the second UV radiation process, the cap layer 40 may also beexposed to IR radiation. The exposure of the cap layer 40 to IRradiation may include IR radiation from one or more IR lamps, one ormore IR LEDs, or one or more IR lasers, or a combination of two or morethereof. The IR radiation may range in wavelength from approximately 1micron to approximately 25 microns. Desirably, the IR radiation mayrange in wavelength from approximately 8 microns to approximately 14microns.

Following the second UV radiation process, the cap layer 40 mayoptionally be thermally treated by elevating the temperature of thesubstrate to a thermal treatment temperature ranging from approximately200 degrees C. to a temperature less than the thermal decompositiontemperature of the sacrificial layer 30. If no sacrificial layer 30exists on the substrate, higher thermal treatment temperatures may bepermitted.

The thermal treatment of the dielectric film, following the first UVradiation process and the second UV radiation process, may be performedin the same processing system, as the UV exposure(s). Alternatively, thethermal treatment of the cap layer 40, following the first UV radiationprocess and the second UV radiation process, may be performed in adifferent processing system than the UV exposure(s).

Referring now to FIG. 5, a UV exposure system 400 is shown according toanother embodiment. UV exposure system 400 includes a process chamber410 configured to produce a clean, contaminant-free environment fortreating a substrate 425 resting on substrate holder 420. UV exposuresystem 400 further includes one or more radiation sources configured toexpose substrate 425 having the dielectric film to electro-magnetic (EM)radiation at single, multiple, narrow-band, or broadband EM wavelengths.The one or more radiation sources can include an optional IR radiationsource 440 and a first UV radiation source 445. The exposure of thesubstrate to UV radiation and optionally IR radiation can be performedsimultaneously, sequentially, or over-lapping one another. Additionally,the one or more radiation sources may include a second UV radiationsource 446 configured to irradiate substrate 425 at a wavelength, orrange of wavelengths, different than the first UV radiation source 445,or different than the first UV radiation source 445 and overlapping withthe first UV radiation source 445.

The IR radiation source 440 may include a broad-band IR source, or mayinclude a narrow-band IR source. The IR radiation source may include oneor more IR lamps, one or more IR LEDs, or one or more IR lasers(continuous wave (CW), tunable, or pulsed), or any combination thereof.The IR power may range from approximately 0.1 mW to approximately 2000W. The IR radiation wavelength may range from approximately 1 micron toapproximately 25 microns and, desirably, can range from approximately 8microns to approximately 14 microns. For example, the IR radiationsource 440 may include an IR element, such as a ceramic element orsilicon carbide element, having a spectral output ranging fromapproximately 1 micron to approximately 25 microns, or the IR radiationsource 440 can include a semiconductor laser (diode), or ion,Ti:sapphire (Al₂O₃), or dye laser with optical parametric amplification.

The first UV radiation source 445 (and the second UV radiation source446) may include a broad-band UV source, or may include a narrow-band UVsource. The first and second UV radiation sources 445,446 may includeone or more UV lamps, one or more UV LEDs, or one or more UV lasers(continuous wave (CW), tunable, or pulsed), or any combination thereof.UV radiation may be generated, for instance, from a microwave source, anarc discharge, a dielectric barrier discharge, or electron impactgeneration. The UV power density may range from approximately 0.1 mW/cm²to approximately 2000 mW/cm². The UV wavelength may range fromapproximately 100 nm to approximately 600 nm and, desirably, may rangefrom approximately 200 nm to approximately 400 nm. For example, thefirst UV radiation source 445 (and the second UV radiation source 446)may include a direct current (DC) or pulsed lamp, such as a Deuterium(D₂) lamp, having a spectral output ranging from approximately 180 nm toapproximately 500 nm, or the first UV radiation source 445 (and thesecond UV radiation source 446) may include a semiconductor laser(diode), (nitrogen) gas laser, frequency-tripled Nd:YAG laser, or coppervapor laser.

The IR radiation source 440, or the first and second UV radiationsources 445,446, or both, may include any number of optical devices toadjust one or more properties of the output radiation. For example, eachsource may further include optical filters, optical lenses, beamexpanders, beam collimators, etc. Such optical manipulation devices asknown to those skilled in the art of optics and EM wave propagation aresuitable for the invention.

The substrate holder 420 can further include a temperature controlsystem that can be configured to elevate and/or control the temperatureof substrate 425. The temperature control system can be a part of athermal treatment device 430. The substrate holder 420 can include oneor more conductive heating elements embedded in substrate holder 420coupled to a power source and a temperature controller. For example,each heating element can include a resistive heating element coupled toa power source configured to supply electrical power. The substrateholder 420 may optionally include one or more radiative heatingelements. The temperature of substrate 425 can, for example, range fromapproximately 20 degrees C. to approximately 500 degrees C., anddesirably, the temperature may range from approximately 200 degrees C.to approximately 400 degrees C.

A heating device may be utilized to elevate the temperature of substrate425. The heating device may comprise the thermal treatment device 430 orthe IR radiation source 440 or both.

Additionally, the substrate holder 420 may or may not be configured toclamp substrate 425. For instance, substrate holder 420 may beconfigured to mechanically or electrically clamp substrate 425.

Referring again to FIG. 5, UV exposure system 400 can further include agas injection system 450 coupled to the process chamber 410 andconfigured to introduce a purge gas to process chamber 410. The purgegas can, for example, include an inert gas, such as a noble gas ornitrogen. Alternatively, the purge gas can include other gases, such asfor example H₂, NH₃, C_(x)H_(y), or any combination thereof.Additionally, UV exposure system 400 can further include a vacuumpumping system 455 coupled to process chamber 410 and configured toevacuate the process chamber 410. During a decomposition or curingprocess, substrate 425 can be subject to a purge gas environment with orwithout vacuum conditions.

Furthermore, UV exposure system 400 can include a controller 460 coupledto process chamber 410, substrate holder 420, thermal treatment device430, optional IR radiation source 440, first and second UV radiationsources 445,446, gas injection system 450, and vacuum pumping system455. Controller 460 includes a microprocessor, a memory, and a digitalI/O port capable of generating control voltages sufficient tocommunicate and activate inputs to the UV exposure system 400 as well asmonitor outputs from the UV exposure system 400. A program stored in thememory is utilized to interact with the UV exposure system 400 accordingto a stored process recipe. The controller 460 can be used to configureany number of processing elements (410, 420, 430, 440, 445, 446, 450, or455), and the controller 460 can collect, provide, process, store, anddisplay data from processing elements. The controller 460 can include anumber of applications for controlling one or more of the processingelements. For example, controller 460 can include a graphic userinterface (GUI) component (not shown) that can provide easy to useinterfaces that enable a user to monitor and/or control one or moreprocessing elements.

The controller 460 may be implemented as a DELL PRECISION WORKSTATION610™. The controller 460 may also be implemented as a general purposecomputer, processor, digital signal processor, etc., which causes asubstrate processing apparatus to perform a portion or all of theprocessing steps of the invention in response to the controller 460executing one or more sequences of one or more instructions contained ina computer readable medium. The computer readable medium or memory forholding instructions programmed according to the teachings of theinvention and for containing data structures, tables, records, or otherdata described herein. Examples of computer readable media are compactdiscs, hard disks, floppy disks, tape, magneto-optical disks, PROMs(EPROM, EEPROM, flash EPROM), DRAM, SRAM, SDRAM, or any other magneticmedium, compact discs (e.g., CD-ROM), or any other optical medium, punchcards, paper tape, or other physical medium with patterns of holes, acarrier wave (described below), or any other medium from which acomputer can read.

The controller 460 may be locally located relative to the UV exposuresystem 400, or may be remotely located relative to the UV exposuresystem 400 via an internet or intranet. Thus, the controller 460 canexchange data with the UV exposure system 400 using at least one of adirect connection, an intranet, and the internet. The controller 460 maybe coupled to an intranet at a customer site (i.e., a device maker,etc.), or coupled to an intranet at a vendor site (i.e., an equipmentmanufacturer). Furthermore, another computer (i.e., controller, server,etc.) can access controller 460 to exchange data via at least one of adirect connection, an intranet, and the internet.

Furthermore, embodiments of this invention may be used as or to supporta software program executed upon some form of processing core (such as aprocessor of a computer, e.g., controller 460) or otherwise implementedor realized upon or within a machine-readable medium. A machine-readablemedium includes any mechanism for storing information in a form readableby a machine (e.g., a computer). For example, a machine-readable mediumcan include such as a read only memory (ROM); a random access memory(RAM); a magnetic disk storage media; an optical storage media; and aflash memory device, etc.

As described above with reference to FIGS. 4A through 4E, the first UVexposure process and the second UV exposure process may be performed inthe same UV exposure system (such as UV exposure system 400 in FIG. 5).Alternatively, the first UV exposure process and the second UV exposureprocess may be performed in separate UV exposure systems (each of whichmay include components illustrated in FIG. 5). The UV exposure systemmay be coupled to a multi-element manufacturing system via a transfersystem configured to transfer substrates into and out of the UV exposuresystem. For example, the multi-element manufacturing system can permitthe transfer of substrates to and from processing elements includingsuch devices as etch systems, deposition systems, coating systems,patterning systems, metrology systems, and other material processingsystems.

Although only certain exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention.

1. A method for forming an air gap structure on a substrate, comprising:forming a sacrificial layer on a substrate, wherein said sacrificiallayer comprises a decomposable material that thermally decomposes at athermal decomposition temperature above approximately 350 degrees C.;forming a cap layer on said sacrificial layer at a substrate temperatureless than said thermal decomposition temperature of said sacrificiallayer; decomposing said sacrificial layer by performing a first exposureof said substrate to ultraviolet (UV) radiation and heating saidsubstrate to a first temperature less than said thermal decompositiontemperature of said sacrificial layer; removing said decomposedsacrificial layer through said cap layer; and curing said cap layer tocross-link said cap layer by performing a second exposure of saidsubstrate to UV radiation and heating said substrate to a secondtemperature greater than said first temperature.
 2. The method of claim1, wherein said first temperature causes substantially low photochemicalreaction rates for said first UV exposure in said cap layer.
 3. Themethod of claim 1, wherein said sacrificial layer thermally decomposesat a thermal decomposition temperature above approximately 375 degreesC.
 4. The method of claim 1, wherein said sacrificial layer thermallydecomposes at a thermal decomposition temperature above approximately425 degrees C.
 5. The method of claim 1, wherein said first temperatureis less than approximately 350 degrees C.
 6. The method of claim 1,wherein said first temperature is less than approximately 325 degrees C.7. The method of claim 1, wherein said first temperature is less thanapproximately 300 degrees C.
 8. The method of claim 1, wherein saidfirst exposure of said substrate to UV radiation comprises exposing saidsubstrate to UV radiation from one or more UV lamps, or one or more UVlasers, or both.
 9. The method of claim 1, wherein said first exposureof said substrate to UV radiation comprises exposing said substrate toUV radiation ranging from approximately 100 nanometers to approximately600 nanometers.
 10. The method of claim 1, wherein said first exposureof said substrate to UV radiation comprises exposing said substrate toUV radiation ranging from approximately 170 nanometers to approximately320 nanometers.
 11. The method of claim 1, wherein said second exposureof said substrate to UV radiation comprises exposing said substrate toUV radiation from one or more UV lamps, or one or more UV lasers, orboth.
 12. The method of claim 1, wherein said second exposure of saidsubstrate to UV radiation comprises exposing said substrate to UVradiation ranging from approximately 100 nanometers to approximately 600nanometers.
 13. The method of claim 1, wherein said second exposure ofsaid substrate to UV radiation comprises exposing said substrate to UVradiation ranging from approximately 170 nanometers to approximately 240nanometers.
 14. The method of claim 1, wherein said first exposure ofsaid substrate to UV radiation and said second exposure of saidsubstrate to UV radiation are performed in the same processing chamber.15. The method of claim 1, wherein said first exposure of said substrateto UV radiation comprises exposing said substrate to UV radiation at afirst UV wavelength range, and said second exposure of said substrate toUV radiation comprises exposing said substrate to UV radiation at asecond UV wavelength range.
 16. The method of claim 1, wherein saidfirst UV wavelength range is different than said second UV wavelengthrange, and wherein said first UV wavelength range overlaps with saidsecond UV wavelength range.
 17. The method of claim 1, wherein saidsacrificial layer comprises P(npMA-co-EGDA), and wherein said cap layercomprises a porous material.
 18. A processing system for preparing anair gap structure on a substrate, comprising: a processing chamberconfigured to provide a vacuum environment for a substrate; a substrateholder coupled to said processing chamber, and configured to supportsaid substrate; a first ultraviolet (UV) radiation source configured toexpose said substrate to a first spectrum of UV radiation; a second UVradiation source configured to expose said substrate to a secondspectrum of UV radiation; and a heating device configured to elevate thetemperature of said substrate.
 19. The processing system of claim 18,wherein said heating device comprises a heating element coupled to saidsubstrate holder, or an infrared (IR) radiation source coupled to saidprocessing chamber, or both.
 20. The processing system of claim 18,wherein said first UV radiation source is configured to irradiate saidsubstrate at said first UV spectrum in order to assist the decompositionof a sacrificial layer on said substrate, and said second UV radiationsource is configured to irradiate said substrate at said second UVspectrum in order to cure a cap layer, and wherein said cap layer isformed on said sacrificial layer prior to decomposing said sacrificiallayer.